There were scuba divers in the late 50s early 60s. Scuba is just the first letters of 'self contained underwater breathing appparatus', a term well understood back then, and used to describe the equipment. You might hear 'diving with scuba", or 'skin diving with scuba', or just plain 'scuba diver'. by the early 60s.
With all words, it is usage that determins meaning, so nuanced and subtle distinctions over time become standard. There was no scuba in the US in the forties, but there certainly was scuba (used as a description for the equipment) by the 50s. It's confusing, but 'skin diver' is the older term, first used for all divers not dressed in heavy boots, helmets, and tethered to a surface compressor. Eventually it was used interchangebably with scuba diver. Skin diver was the style, and scuba was the equipment, except for breath hold skin divers who did not use scuba. All were generally referred to as skin divers.
Breath holddivers were never called scuba divers, but scuba divers were called skin divers for a long, long time, and sometimes still are. The 'skin' word refers to the lack of heavy canvas dive suits, especially because in the very early days, before good neoprene suits, divers basically wore nothing but a bathing suit.
Aqua Lung is now and was then a regestered patented trade name for a specific company. Nobody said Aqualung diver because it would be like saying BMW motorcycle driver. Scuba, on the other hand is generic, it refers to a type of equipment, not a company. 'Skin' was nothing more than a word used to distinguish heavily suited divers from those diving without such gear. As was pointed out several times, the term 'skin diver' was, for a long time, understood to mean all divers, snorkelers, free divers, scuba divers, etc., who were not using heavy commercial equipment. Old C cards and telephone business directories listed dive shops under the heading "Skin Diving Equipment and Training". It is only in the recent past, for perhaps only 30 years, that skin diver and scuba diver came to have searate and distinct meanings.
